Modulation, which can be broadly defined as a time varying modification of a signal to impart information thereto, is a crucial feature of the design of almost all radio based systems. An effective and well known form of modulation for digital signals, is binary phase shift keying (BPSK). In BPSK one of the two digital states of information is imparted onto a carrier signal by modulating its phase to have two discrete values which are generally separated by 180 degrees (π radians). Whilst such a modulation technique may be efficient it has not previously been ideally suited for applications where low cost and low power consumption are paramount such as in tagging systems, since the known circuitry for generating BPSK is complex and consumes too much electrical power for operation from a finite battery supply.
The present invention has arisen in an endeavour to provide a modulator circuit which at least in part overcomes the limitations of the known modulators and which is suitable for use in a tagging systems or other applications where low power consumption and circuit simplicity are of importance.